A ship that is not carrying cargo sails while being loaded with ballast water in order to stabilize the ship, and discharges the ballast water in a marine area in which cargo is loaded on the ship.
The ballast water is normally discharged in a marine area different from the marine area where the cargo is loaded on the ship. Thus, microorganisms such as planktons and bacteria contained in the ballast water may be carried to a marine area different from the native habitat of the microorganisms, disadvantageously posing problems such as disruption of ecosystem.
To deal with such problems, international rules for the regulation of ballast water have been formulated, and the International Convention for the Control and Management of Ship's Ballast Water and Sediments (Ballast Water Management Convention) has been adopted.
In the “Guidelines for Ballast Water Sampling (G2)”, “Ballast Water Discharge Standards (D-2)” related to the Ballast Water Management Convention, the allowable population of microorganisms contained and living in the ballast water discharged from the ship is specified for each type of microorganisms based on the minimum size. For example, the allowable population is specified as at most 10/m3 for microorganisms with a minimum size of at least 50 μm (hereinafter referred to as “L size organisms”) and as at most 10/mL for microorganisms with a minimum size of at least 10 μm and less than 50 μm (hereinafter referred to as “S size organisms”).
As a method for measuring microorganism cells living in water such as ballast water, a method described in Patent Literature 1 has been known.
In the method described in Patent Literature 1, first, a chemical substance reacting with an enzyme or a coenzyme present in living cells of microorganisms to generate a fluorescent substance in the cells is allowed to act on a measurement target sample containing the microorganisms. The chemical substance and the microorganisms are then mixed and contacted with one another for given time, and the sample is irradiated with light with a wavelength needed to excite the fluorescent substance generated in the cells. Furthermore, in this method for measuring the living cells of the microorganism cells, light emitted by the individual microorganisms in the sample is measured as the number of points.
This method significantly reduces measurement time that needs to be 10 hours to several tens of hours in a conventional agar culture method, to at most 10 minutes. Furthermore, since means for optically and electrically detecting and measuring light emitted by viable bacteria as points has been established, the number of viable bacteria can be directly, automatically counted. Thus, advantageously, a sterilization apparatus can be promptly controlled, and product quality can be expeditiously managed.
However, in the method described in Patent Literature 1, measured values may vary depending on the type of water, temperature, the type of a stain, concentration, staining time, and the like.
As other methods, for example, the following are known: an examination apparatus for microorganisms that passes sea water pumped up using a water pump through flow cells and performs image measurement in order to determine whether or not the discharge standards are met when the ballast water is discharged (for example, Patent Literature 2), and an examination apparatus for microorganisms which passes sea water pumped up using a water pump through filter units with different apertures and which allows microorganisms on the filters to emit light to count the number of the microorganisms (for example, Patent Literature 3).
The examination apparatus for microorganisms described in Patent Literature 2 includes a staining section that allows a liquid specimen to flow while staining organisms with living cells present in the specimen, a concentration section that allows the stained specimen to flow while concentrating the specimen so as to increase the concentration of the organisms, an individual measurement section that acquires image information on individuals including the organisms in the concentrated specimen, and control means for measuring the organisms based on the image information on the individuals output by the individual measurement section.
This allows sequential execution of a staining step of staining the organisms in the liquid of the specimen, a step of concentrating the organisms in the liquid, a step of acquiring information on the organisms in the liquid, and the like. Thus, compared to a technique for individually executing schemes, this technique has the following advantages. Waiting time until a part of a specimen on which one step has been executed proceeds to the next step can be drastically reduced or eliminated. Furthermore, information indicating whether the organisms are alive or dead can be acquired, the information being stable in a sense that the condition of staining during the waiting time is prevented from being degraded.
However, the examination apparatus for microorganisms described in Patent Literature 2 sequentially passes sea water pumped up using the water pump through various steps, leading to the need for a large-scale apparatus and increased manufacturing costs. At least several hours may be needed to complete the measurement.
Furthermore, the examination apparatus for microorganisms described in Patent Literature 3 is characterized by including a step of passing sea water though filter units with three types of filters arranged in series and having different apertures, a step of causing the microorganisms collected and living in the filters to perform one of color production, light emission, and fluorescence production, and a step of detecting one of the color production, light emission, and fluorescence production and counting the number of the microorganisms in the ballast water or sea water by means of image analysis.
Thus, the microorganisms can be captured according to the stepwise size thereof, consequently enabling expeditious determination of whether allowable residue standards regulated according to the size of microorganisms are met.
However, as is the case with Patent Literature 1, the examination apparatus for microorganisms described in Patent Literature 3 passes sea water pumped up using the water pump through various steps, possibly leading to the need for a large-scale apparatus and increased manufacturing costs.